Marie Severin was born in East Rockaway, New York, on Long Island, the second and last child of a father born in Oslo, Norway, who immigrated to the United States at age 3, and a mother, Peg, from Syracuse, New York, whose heritage was Irish. Her older brother, John Severin, was born in 1922. The family moved to Brooklyn, New York City, when Marie was 4. She attended a Catholic grammar school and then the all-girl Bishop McDonnell Memorial High School. The family lived in an apartment in the Bay Ridge neighborhood at the time; it is uncertain if this was the family's original Brooklyn locale from Severin's childhood or if the family moved to that neighborhood in the interim. Due to the high school's staggered schedule, Severin's class graduated in January 1948, rather than in the spring as typical.
Severin grew up in an artistic household where her father, a World War I veteran, eventually became a designer for the fashion company Elizabeth Arden during the 1930s. In her teens, Severin took "a couple of months" of cartooning and illustration classes, and attended Pratt Institute in Brooklyn "for one day and said, 'This is a college', and I wanted to draw and make money". Her first job was doing clerical work for an insurance company in downtown Manhattan "for a couple of years" while still living at home.